Automatic control of free-piston gas-generators



AUTOMATIC CONTROL OF FREEPISTON GAS-GENERATORS Filed April 10, 1958 BY Osc/13 AWEER United States Patent O AUTOMATIC CONTROL OF FREE-PISTON GAS-GENERATORS Oscar Huber, Sainte-Foy-les-Lyon, France, assignor to Societe dEtudes et de Participations Eau, Gaz, Electricite Energie SA., Geneva, Switzerland, a society of Switzerland Applicatie April 1o, 195s, serial No. 121,136 6 claims. (ci. 12s- 46) The present invention relates to the automatic control of free-piston gas-generators.

By the term free-piston gas-generator is meant a machine comprising an internal-combustion-operated free piston engine part which usually works as a two-stroke engine with self-ignition of the fuel (diesel), and a compressor part which is driven by the engine and which compresses air in a compressor cylinder, all or some of the compressed air being used to supply and scavenge the engine, and the compressor delivering through its delivery ports hot gas under pressure which forms the power gas for a receiving machine, such as a turbine.

The energy developed in the engine part serves to drive on its power stroke at least one piston assembly,

formed by anengine piston and a compressor piston, the piston assembly being moved in the opposite direction by a pneumatic return-energy accumulator or cushion which stores at least some of the energy developed by combustion of the fuel during the power stroke.

As a rule, a machine of the kind described is controlled both by pressure impulses d erived from the receiving machine driven by the power gas and also by pressure impulses derived from the gas-generator itself, the latter impulses being known as internal impulses. These usually act upon a member knownas a stabiliser which controls the amount of `air contained in the cushion. 1

It is known to control the stabiliser in dependence both upon an operating pressure ofthe gas-generator, that is to say the pressure either of the scavenge air compressed by the compressor or of the power gas issuing from the engine, and also upon a pressure supplied by the cushion and which will be sometimes referred to hereinafter as the characteristic pressure of the cushion.

It is also known tol vary the amount of air in the cushion so that the ratio between `the rtinal value of compression in the engine and the intake pressure of the compressor increases at least during normal running of the gas-generator when the said operating pressure increases and vice versa.

`It is theprincipal object of the present invention to provide a gas-generator in `which the automatic control means produce a great variation of the final value of the compression pressure in theengine not only in response to variation in the gas delivery pressure but also in' response to variation of the amplitude of reciprocation,ri.e., length of stroke, of the piston assembly.

For this purpose, according to the present invention, in a free-piston gas-generator as above referred to, said characteristic pressure of the cushion is the pressure existing therein at a predetermined point in the stroke of the piston assembly.

- Other features of the invention will be apparent from the following description with reference to the accompanying drawing in which there is shown a diagrammatic view in axial section of a free-piston gas-generator`according to the invention.` The gas-generator is preferably arranged so that the 2,926,642 Patented Mar. 1, 1960 lCe compressor draws in air during the power stroke, that is to say during the stroke resulting from the combustion of fuel in the engine, while the compression of the air in the compressor and of the combustion air in the engine cylinder are effected during the return stroke produced by the energy stored in the cushion, the :return energy representing most of the combustion energy produced during the power stroke.

Thus, the gas-generator diagrammatically illustrated in the drawing comprises at least one compressor cylinder 1 and. one engine cylinder 2, and a piston assembly formed byva `compressor piston 3 and an engine piston 4 which operates in the two cylinders 1 and 2.

The part of the cylinder 1 adjoining the engine cylinder 2 is provided with inlet valves 5 and delivery valves 6, the latter being fitted in a partition 7 which forms the internal head plate of the compressor cylinder 1 and which separates the same from a scavenge air reservoir 8 forming an engine case surrounding the engine cylinder 2. The compressor cylinder proper is formed by a chamber a located between the piston 3 and the partition 7. On the other hand, the pneumatic return-energy accumulator or cushion is formed by a chamber b located between the head 9 of the compressor cylinder and the piston 3.

Intake portsl() and exhaust ports 11, controlled by the engine piston 4, are provided in the wall. of the engine cylinder 2. Connected to the exhaust ports 11 is an exhaust pipe 12 through which the power gas constituted by the excess of scavenging air and by the combustion gas of the engine cylinder are conveyed to a receiving machine such as a turbine (not shown).

The engine cylinder 2 is fitted with a fuel-injector 13 supplied from aninjection pump 14 through a pipe 15. The compression which is produced in the engine cylinder 2 when the piston assembly 3, 4 has terminated its inward stroke (to the right in the drawing) is high enough for the fuel injected by the injector 13 to be ignited by the heat ofscornpression alone without the use of any special ignition device. The engine part is a two-stroke engine operating on the diesel principle.

In the gas-generator illustrated in the drawing, the injection pump 14 is driven by means of a rocking lever 16 which is driven by the piston assembly 3, 4 through the agency of a rod 17 and link 18.

For the sake of simplicity in the description and draw` ing, a gas-generator having only one piston assembly 3, 4

`has been described and illustrated but, as is usual in practice, the gas-generator will generally comprise two such assemblies which move in opposite directions in a single engine cylinder, the compressor pistons operating i in compressor cylinders disposed on either side of the Ofcourse, the invention is equally` engine cylinder. applicable to the latter kind of gas-generator.

Some of the means for controlling a gas-generator of the kind described take the form of means for controlling the quantity of fuel injected into the cylinder 2. Such means comprise, for instance, a regulating member 19 which determines the quantity of Vfuel delivered per cycle by the pump 14 and injected by the injector and which may, in knownlmanner, take the form of a toothed rack which rotates the piston (not shown) of the injection pump.` The member 19 is controlled in known manner to increase or decrease the fuel delivery by means of a regulator (not shown) driven by the receiving machine (turbine) and acting on the member `19 through a linkage, or through a hydraulic, electrical, or other means, in dependence upon the speed of-the receiving machine. However, this controlin dependenceupon the speed of the receiving machine must remain within limits whose values are dependent upon the operating pressure, or a similar operating factor, of the gas-generator, such limits being defined by a lever adapted to rotate around a "spindle 2l`a`nd hvingone of 'its ends articulated to the control linkage of the member 19, the other end of the lever 20 comprising .twp .ca m surfaces 22, 23, a stop 24being provided `betwen` the two cam surfaces 22 and 23, the position of thestop 24 being controlled by means -t`o be described hereinafter.'

Means for controlling the amount of air in the cushion b take the form of a ymember known as a stabiliser and formed by a hollow slide valve 25 adapted to move inside a cylinder 26 disposed insidethe engine-case. "he slide valve 25 is divided by a lpartition into two chambers, one of which is provided with Vnon-return valves 28 which only open in such a way as to Vallow the passage of air'from' the ,engine-case 8 intothe slide valve 2S, While the non-return`valves 2 9 of the other chamber open only in the opposite direction VVso that air can flow out of the slide valve 25into thefengine-case 8. The lateral wall of each of the ltw'o" chambers is formed with van aperture 30, 3i, thesefapertures serving, in dependence upon the `axial position of `-the slide valve 25,'to connect one'or the other of the last-mentioned chambers to a pipe 32 connecting the cylinder 26 to the cushion b. The ,slide valve 25, in its central position (that shown in the figure), cuts oi its two chambers completely from the pipe 32. Thus, according to its axialposition, the slide Valve 25 either allows air to escape from the cushion b into the engine-case 8 through the non-return valves 29 or permits air toreturn from the reservoir into the cushion through the non-return valves 28 or it enables the quantity of air in the accumulator b to'be maintained constant.

The automatic stabiliser control just described is effected by means of internal pressure impulses, that is, impulses derived from the prime mover. These impulses are the pressure in the engine-case 8 and the characteristie pressure of the cushion b. The two last-mentioned pressures act upon a stepped piston 33 which is rigidly secured to the slide valve 25 and upon one of the surfaces sl of whichacts the characteristic pressure of the cushion b, while the other surface s2 (s2 being less than s1 is subjected to the pressure in the engine-case 8. The piston 33 is disposed in a cylinder 34 to which are connected a pipe 35 for placing the top ofthe cylinder 34 in communication with theHengine-case 8, and a pipe 36 through which the characteristic pressure of the cushion b is applied to the bottom of the cylinder 34.

The ratio between the surfaces s1 and s2 is such that the stabiliser controls the amount of air in the cushion so that the iinal compression pressure-in the engine cylinder increases when the operating pressure, that is to say the pressure in the engine-case 8, increases, and decreases when this operating pressure decreases, the intake pressure in the compressorv cylinder y(as supplied through the valves 5) being assumed to be constant. ,Therefore, an increase or decrease in the value of final compression in the engine cylinder causes a corresponding variation in the ratio between the iinal value or compression in the engine cylinder and the intake pressure in the compressor cylinder. One effect of such a variation of the said ratio is to reduce the number of reciprocations lper unit of time'of the piston assembly when the operating pressure 'decreases and to increase this number when the operating pressure increases. Since the turbine forming the receiving machine of the gas-'generator requires not only high pressures but also high delivery rates for heavy loads and vice versa, this variation'of the number of reciprocations of the piston assembly in dependence upon the operating pressure corresponds exactly to turbine requirements and helps to reduce the difference between the minimum and maximum Vstrokes of the piston assembly.

Where itis required to vary the final compression pressure in lthe engine cylinder in themanner hereinbefore stated, it has already been proposed to use as characteristic `pressure`of 'the cushion the mean pressure therein. However, in this case, the range of variation of the final compression pressure for a given range of variation of the operating pressure depends practically only upon this variation of the operating pressure, whereas variations in the length of stroke of the piston assembly are practically without influence upon said Afinal compression variation.

As already `stated it is Vthe principal object of the invention to make the variation of ythe final compression pressure in the engine cylinder responsive also to `variation of the length of stroke. To this end according to the main featurerof my invention, I use, as characteristic pressure of the cushion, an instantaneous pressure derived from the cushion when "the piston 3 operating therein is in a predetermined position.

As the receiving machine isa turbine, .an increase in the operating pressure generally Valso.involves aniucrease in the length of kstroke and 'vice versa, .whereby l said feature of my invention .permits of'obtaining apmuch more important variation of the iinal compression pressure in the engine cylinder fora given variation of the operating pressure. For instance, owing to the use of this characteristic pressure, variations in the final cornpression pressure in the engine cylinder offrom 30 ktoll() atmospheres are possible for a variation of the operating pressure of from .aboutlfto 31/2 atmospheres accompanied by a variation ofthe length of stroke capable of complying with the requirements of the turbine.

ln order thata4 pressure derivedfrom the cushionb mayact upon the surface s1 ofthe stepped piston 33, the pipe 36 connecting the cushion b to the bottom of the cylinder 34 is controlled by a member rigidly secured to the piston assembly 3, 4 for instance by a rod 37 secured to the assembly 3, 4 and sliding in a tubular gu-ide 38 fitted to therhead 9 of the cylinder'l, the guide 38 forming an interruption in the pipe 36.` The rod 37 is formed with a duct 39 which, when the piston assembly 3, 4, is in a predetermined position, interconnects those two parts of the ypipe 36 which are upstream and downstream of the guide 38. Hence only when the piston assembly 3, 4 is in this predetermined position can the pressure which exists at that moment in the cushion b be transmitted through the pipe 36 to act on the bottom of the piston 33, the pipe 36 being closed when the moving assembly is in any other position.

The difference between theminirnum and maximum values of the final compression pressure in the engine cylinder for la given range of operating pressures can be increased further by another arrangement.

According to this arrangement, the lower part of the cylinder 34, or, even better, the pipe 36 downstream of its control member 38, 39 is formed with a bleed-oit connection which opens before the free piston reaches its maximum outer dead point, ,preferably at the instant when the piston is near its minimumouter dead point, and

which remains open for as long as the piston is beyond the position at which the bleed-off connection is opened, the amount of air flowing through the bleed-ott' thus increasing in proportion as thestroke lot the piston is ex tended beyond the position of opening. `It should be noted that, above a -low-load speedV during which the stroke is constantly maintained at its minimum value, the stroke is increased beyond this minimum value in proportion as the operating pressure increases. The effect of the bleed-oli therefore increases in proportion yas the operating pressure increases, the bleed causing the operating pressure in the engine case to predominate increasingly over the pressure reduced by the bleedoft`,the latter pressure corresponding to the characteristic cushion pressure.

In the gas-generatorshownin the drawing, the bleed-oli connection takes the form of a calibrated aperture 40 in a pipe 41 which opens atout? 6nd Ainto` the pipe '3,6 downstream of the region where the same is controlled by the rod 37, and which opens at its other end into the tubular guide 38 opposite a recess 42 formed therein. Also, one end of the duct 39 opens into a longitudinal groove 43 in the rod 37, the slot 42 and groove 43 being so disposed and having lengths such that the pipe 41 starts to be placed in communication with the atmosphere, by way of the groove 43, duct 39 and recess 42, at the instant when the piston assembly 3, `4 reaches its outer dead point corresponding to the minimum stroke, this communication with the atmosphere being maintained for as long as the moving assembly is beyond the outer dead point position corresponding to the minimum stroke. v

Advantageously, whatever the means employed for controlling the `stepped piston 33 in dependence upon the operating pressure and upon the characteristic accumulator pressure, a spring 44 acts upon the stepped piston with a force which is preferably variableby means of a hand wheel 45 or other means controllable by the supervising operator. The force of the spring 44is increased by compressing it during the starting period to produce, during this period, final compression pressuresl greater than those normally obtained at low pressures, in order that the fuel may be ignited during this period when the machine is relatively cold. l

According to an additional feature, the characteristic pressure derived from the cushion when the piston assembly 3, 4 is in a predetermined position is used to control not only the stabiliser but also the timing of fuel injection in the engine part of the gas-generator and/or the device which determines the lower and/or upper limits of the zone in which the regulator of the receiving machine (turbine) can move the regulating member `of the injection pump of the gas-generator.

For instance, in the gas-generator shown in the drawing,` the pressure derived from the cushion b when the piston assembly is in a predetermined position is transmitted not only into the bottom of the cylinder 34, to control the stabiliser, but also, by way of a pipe 46, into a cylinder 47 Where it acts, against a return spring 48, upon a piston 49 having a rod 50 bearing the stop 24 which determines the limitsof the zone in which the impulse derived from the receiving machine can move the control member 19 of the injection pump 14. The rod 50 also bears a pin 51 which controls, by way of a fork 52, an eccentric 53 around which can pivot the lever 16 driving the piston of the injection pump 14. By` rotating the eccentric 53, the rod 50 changes the timing of the injection of fuel into the engine cylinder 2 by the injector 13. In a general manner, while I have, in the above description, disclosed what I deem to be practical and efficient embodiment of my invention, it should be well understood that `I do not wish to be limited thereto as there might be changes made in the arrangement, disposition and form of the parts without departing from the principle of the present `invention as comprehended within the scope of the accompanying claims.

What Iclaim is: p t

l. A free piston auto-generator which comprises, in combination, an engine part and a compressor part, said engine part including an engine cylinder and an engine piston movable in said cylinder, said compressor part including a compressor cylinder mounted in fixed position with respect to said engine cylinder and a compresser piston rigid witl` said engine piston and movable in said compressor cylinder, a casing in temporary communication with said engine cylinder for feeding cornpressed air thereto, said compressor piston forming with the portion of said compressor cylinder closer to said engine cylinder an air compression chamber, valve means for connecting said air compression chamber with the atmosphere 4on every outward stroke of said engine piston and with said casing on every return'stroke of said engine piston, said compressor piston forming, with the other portion of said compressor cylinder an air cushion chamber in which air is compressed during every outward stroke of said engine piston, whereby expansion of said air` cushion produces every return stroke of said engine piston, a conduit having fone end in communication with said air cushion chamber, a stabiliser valve mounted to control the communication between the other end of said conduit and said casing, said stabiliser valve ineluding a cylindrical housing, a member slidable in said housing and having a neutral position therein and check valve means carried by said member arranged to open an unidirectional communication from said casing to said conduit when saidmember is moved in one direction from said neutral position thereof and an unidirectional communication from said conduit to said casing when said member ist, moved in the other directionfrom said neutral position thereof, means operative by `a pressure at least substantially proportional to the pressure in said casing for urging said member in said first mentioned direction, ,means forming a space containing air under pressure supplied from said cushion air chamber, means operative by the pressure in said space for urging said member in said second mentioned direction, and means forallowing air to leak out from said space, said last mentioned means being operatively connected with said compressor piston so as to be operative for all positionsl of said piston between a predetermined position thereof and its outer dead point position. Y

2. `A free piston auto-generator which comprises, in combination, an engine parranda compressor part,` said engine part including an engine cylinder and an enginev piston movable in said cylinder, said compressor part including a compressor cylinder mounted in fixed position with respect to said engine cylinder and a compressor piston rigid with said engine piston and movable insaidcompressor cylinder, a casing in temporary communication with said Vengine cylinder for feeding compressed air` thereto, said compressor piston forming withL the portion of said compressor cylinder closer` to said engine cylinder an air compression chamber, valve means forconnecting said air compression chamber with the atmosphere on every outward stroke of` said engine piston and with said casing on Veveryreturn stroke of said enginepiston, said compressor piston forming with the other portion of said compressor cylinder an air cushion chamber in which air is compressed during every outward stroke of said engine piston, whereby expansion of said air cushion produces every return stroke of said engine piston, a conduit having one end in. communication with, said air cushion chamber, a stabilizer valve mounted to control the communication between the other end of said conduit and said casing, said stabilizer valve including a cylindrical housing, a member slidable in said housing, and having aneutral position therein and check valve means carried` by said member arranged to open an unidirectional communication fromV said casing to said conduit when said member is moved in one direction fro n said neutral position thereof and an unidirectional communication from said conduit to said casing when said member is moved in the other direction from said neutral position thereof, a cylinder closed at both ends located in line with said cylindrical housing and in fixed position with respect thereto, a piston slidable in said last mentioned cylinder rigidly `connected with said member, a conduit extending between said casing and one end of said last mentioned cylinder so that the pressure transmitted from said casing through said last mentioned conduit urges said piston and therefore said member in said rst mentioned direction, a conduit leading into the other end of said last mentioned cylinder, valve means `operative by said compressor piston for connecting said last mentioned conduit with-said air cushion chamber for-a given position of said compressor piston with'respect to saidl compressor cylinder,

leak means, including a calibrated passage for connecting said last mentioned conduit with the atmosphere, and.

f t`7 v'lverneans operatively eonnected'wit'h said compressor piston `for opening said "leak means for all positions 'of said pistonbe'tweren a predetermined position thereof and its outer dead point position.

3.`A free pistonVauto-generator which comprises, in combination, an'enginepart and a compressor part, said engine part including an engine cylinder and an engine piston movable yin said cylinder, lsaid compressor part including a compressor cylinder mounted in iixed position with respect to said engine cylinder and a compres` sor piston rigid with said engine piston and movable in said compressor cylinder, said engine piston and said compressor piston `forming together a composite piston unit, a casing in temporary communication with said engine cylinder for feeding `compressed airthereto, said compressor piston forming with said compressor cylinder and ,air compression chamber, 'valve means for connecting 4said air compression chamber withthe atmosphere on every outward stroke of s'aid engine piston 'and with said 'casing on every return stroke of said engine piston, an air cushion cylinder mounted in fixed position with respect to said cylinders in opposed relation to said Vengine cylinder, an air cushion piston rigid with said composite piston unit and cooperating withvsad air cushion cylinder to form therewith an air 'cushion chamber in which air is compressed during every outward stroke of said engine piston, whereby expansion of said air cushion produces every return stroke ofsaid engine piston, a conduit having one end incommunication with said air cushion chamber, a stabilizer valve mounted to control the communication between the other end of said conduit and said casing, said stabilizer valve including a-cylindrical housing, a member slidable in said housing and having a neutral position therein and check valve means carried by said member arranged to open an undirectional communication from said casing to said conduit when said member is moved in one direction from said neutral positim thereof and an unidirectional communication from said conduit to said casing when said member is moved in the other directionV from said neutral position thereof, means operative 'by a pressure at least substantially proportional to the'pressure in said casing for urging said memberl in said first mentioned direction, means forming a space containing airunder pressure supplied from said vcushion air chamber, means operative by the pressure in said space for urging said member in said second mentioned direction, and means-for allowing air to leal: out from said space, said -last mentioned means being operatively( connected with Asaid 'compressor piston so as to be operative for all positions of said piston between a predetermined positionthereof and its outer dead point position.

4. A free piston auto-generator which comprises, in combination, an engine part and a compressor part, said engine part including an 'engine cylinder and an engine piston movable in said cylinder, said 'compressor part including a compressor cylinder mounted in fixed position with respect to said engine cylinder and a compressor piston 'rigid with said engine piston andv movable in said compressor cylinder, saidl engine 'piston and said compressor piston forming together a composite piston unit, a casing in'temp'orary communication wtih said engine cylinder for feeding compressed air thereto, said compressor piston forming with said compressor cylinder an air compression chamber, valve means for connecting said air compression chamber with the atmosphere on every outward stroke of said engine piston and with said casing on every return stroke V'of said engine piston, an air cushion cylinder mounted in fixed position with respect to 'said cylinders in opposed relation to said engine cylinder, an air cushion piston rigid with said composite pistoni unit 'and' cooperating with said air cushion cylinder to form therewith an air cushion chamber inV which air is compressed during every outward stroke of said engine- Piston, whereby expansion of Said air cushion produces'- 8 every'return stroke of said engine piston, a conduit having one Aend in communication with said air cushion chamber, a stabilizer valve. mounted to control the ccmmunication between the other end of said conduit and said casing, said stabilizer Valve including a cylindrical housing, a member slidable in said housing and having a neutral position therein and check'valve means carried by'said member arranged to open an unidirectional cornmunication from said casing to said conduit when said member is moved in one direction from said neutral position thereof and an unidirectional lcommunication from said conduit to said casing when said member is moved in the other direction from said neutral position thereof, a cylinder closed at both ends located in line with said cylindrical housing and in fixed position with respect thereto, a piston slidable in said last mentioned cylinder rigidly connected with said member, a conduit extending between said casing and one Vend of said last mentioned cylinder so that the pressure transmitted from said casing through said last mentioned conduit urges said piston and therefore said member in said first mentioned direction, a conduit leading into the other end of said last mentioned cylinder, valve means operative by said compressor piston for connecting said last mentioned conduit with saidrair cushion chamber for a given position of said compressor piston with respect to said compressor cylinder, leak means, including a calibrated passage forroonnecting said last mentioned conduit with the atmosphere, and valve means operatively connected with saidcompressor piston for opening said leak means for all positions of said piston between a predetermined position thereof and its outer dead point position.

5. A free piston auto-generator which comprises, in combination, an engine part and a compressorV part, said engine part including an engine cylinder and an engine piston movable in said cylinder, said compressor part including a compressor cylinder mounted in fixed position with respect to said engine cylinder and a compressor piston rigid with said engine piston and movable in saidcompressor cylinder, said engine piston and said compressor piston forming together a composite piston unit, a casing in temporary communication with said engine cylinder l for feeding compressed air thereto, said compressor piston forming with said compressor cylinder an air compression chamber, valve means for connecting said air compression chamber with the atmosphere on every outward stroke of said engine piston and with said casing on every return stroke of Vsaid engine piston, an air cushion cylinder mounted in fixed position with respect to said cylinders in opposed relation to said engine cylinder, an air cushion piston rigid with said composite piston unit and cooperating with said air cushion cylinder to form therewith an air cushion chamber in which air is compressed duringevery outward stroke of said engine piston, whereby expansion of said air cushion produces every return stroke of said engine-piston, a conduitV having one end in communication with said air cushion chamber, a stabilizer valve mounted to control the communication between the other end of said conduit and said casing, said stabilizer valve including a cylindrical housing, a member slidable in said housing and having a neutral position therein and check valve rneans 'carried by said member arranged to open an unidirecti'onal communication fromsaid casing to said conduit when said 'member is moved in one direction from said neutral position thereof and van unidirectional communication yfrom said conduit to said casing when said member is moved in the other direction from said neutral position thereof, means operative by a pressure at least substantially proportional to the pressure in said casing for urging said member in said first mentioned direction, means operative Vby the pressure existing in said air cushion chamber for a lgiven position of said compressor piston with respect ot said compressor cylinder for urging said 'member insaid second mentioned direction, means for injecting' fuel into said engine cylinder, and means Y Y 9 operative by said pressure existing in said air cushion chamber for a given position of said compressor piston with respect to said compressor cylinder for controlling the timing of said fueliinjection means.

6. A free piston auto-generator whichV comprises,'in combination, an engine part and a compressor part, said` air compression chamber, avalve means for connecting said air compression chamber with the atmosphere on every outward stroke of said engine piston and with said casing on every return stroke of said engine piston, an air cushion cylinder mounted in fixed position with respect to said cylinders in opposed relation to said engine cylinder, an air cushion pistonrigid with said composite piston unit and cooperating with said air cushionA cylinder to form therewith an air cushion chamber in `which air is compressed during every outward `stroke of` Said engine piston, whereby expansion of said air cushion produces every return stroke ofsaid engine piston, a `conduit having one end in communication with said air cushion cham-v ber, a stabilizer valve mounted to control `the communication between the other end of said conduit and said casing, said stabilizer valveincluding a cylindrical housing, a member slidable in said housing and having a neutral position therein and checkrvalve means carried by said member arranged to open an unidirectional communication from said casing to said conduit when said member is moved in one direction from said neutral position thereof and an unidirectional communication from said conduit to said casing when Said member is moved in the other direction from said neutral position thereof, means operative by a `pressure at least substantially prop-ortional to the pressure in said` casingfor urging said member in saidrstlmentioned direction, means operative by the pressure existing in said air cushion chamber for a given position of said compressor piston Vwith respect to said compressor cylinder for urging said `member in said secondvrnentioned direction, means for determining the limits of fuel feed of said engine cylinders, and means operative by said pressure existing in saidV air cushion chamber for a given position of said compressor piston with respect to said compressor cylinder for controlling said fuel feed limits determining means.

References Cited in the `file of this patent UNITED STATES PATENTS Australia Dec. 2, 1955 welsh L Aug. 19, 1947 

